This invention relates to a method of manufacturing carbon black. More particularly this invention relates to a method for achieving independent control of the aggregate particle size distribution of a carbon black. Even more particularly, this invention relates to a method whereby the energy efficiency of a carbon black reactor is optimized while, at the same time, controlling the aggregate particle size distribution of the carbon black.
A carbon black reactor is made versatile by having a "make oil" spray position adjustable axially in relation to the downstream direction in the combustion section of the reactor. That is, the make oil spray protrudes into the center of the reactor inside the combustion section, and is cooled by a water jacket or some fluid external to the process. In accordance with a typical operation, fuel and air are burned to the blast section of the reactor to produce hot combustion gases which mix well with the hydrocarbon make oil to produce carbon black.
By moving the make oil spray nozzle position axially, it is well known that the aggregate particle size of the carbon black is affected. Hence, this feature is desirable since it permits a wider variety of blacks to be produced with a given reactor geometry. However, being able to position the make oil spray nozzle along the axis of the reactor, and being able to change the location of the make oil spray nozzle relative to the reactor's "throat", requires a means of cooling the make oil spray as there are no metals able to withstand the reactor temperatures.
The cooling of the make oil spray placed feedrate limitations on the reactor because heat is removed from the reaction zone. Further, a make oil spray which is positioned along the reactor axis limits the versatility of injecting the hydrocarbon feedstock into a plurality of "zones of turbulence".
It is desirable to control the aggregate particle size distribution of the carbon black in order to impart unique performance properties to the black. For carbon blacks that are used in rubber applications, proper control of aggregate particle size distribution insures an optimum combination of rolling resistance, hysteresis, and treadwear properties in automobile tires. The aggregate particle size distribution can range from particles of an SRF type carbon black to particles of an SAF type carbon black. Alone, neither of these types of carbon blacks would have the required inherent properties to satisfy reinforcing requirements in rubber. The mean aggregate particle diameter of a narrow distribution tends to be relatively small, e.g., 10-20 millimicrons, and the mean aggregate particle diameter of a wide distribution tends to be relatively large, e.g., 50-60 millimicrons.
Unless some novel mixing procedure can be had, it is difficult, cumbersome and expensive to blend blacks of different aggregate size distributions. Ideally, these carbon blacks would have to be sized before blending. Of course, blending of several known aggregate size distributions could be done. However, developing and producing the desired blend would require several carbon black reactors and the maintenance of a complex production schedule in order to assure the correct blend. Hence, use of several reactors or blending is both uneconomical and impractical.